The present invention relates to an electrochromic display device.
A display device utilizing an electrochromic phenomenon to display a desired or predetermined pattern is known as an electrochromic display device. The conventional electrochromic display device comprises, in general, an electrolyte filled in a confined space defined between a glass substrate and a counter-substrate, a transparent electroconductive layer deposited on an inner surface of the glass substrate in a configuration corresponding to a pattern to be displayed, and an electrochromic electrode layer made of a material capable of exhibiting an electrochromic phenomenon and deposited on the transparent electroconductive layer on one side opposite to the glass substrate.
In this conventional electrochromic display device, or ECD device, the transparent electroconductive layer is formed directly on the glass substrate in the form of a patterned electrode arrangement whereas the electrochromic electrode layer, or EC electrode layer, is formed by either vapor-depositing or sputtering a solid electrochromic material.
Both the vapor-deposition technique and the sputtering technique require the employment of a complicated and expensive vacuum pump as well as a complicated and time-comsuming process handling. In view of this, there has been proposed a method for forming the EC electrode layer on the transparent electroconductive layer on the glass substrate, which method comprises applying a solution, containing dissolved therein a composition such as a material capable of exhibiting the electrochromic phenomenon when baked, to the transparent electroconductive layer and then baking the coating of the applied solution.
However, since in the manufacture of the ECD device, the transparent electroconductive layer is formed directly on the glass substrate in the form of a patterned electrode arrangement as hereinbefore described, an EC electrode layer is formed directly on the glass substrate at an area where no pattern is formed. If a display pattern is to be formed by etching the EC layer as is, the etching speeds for etching off the EC layer formed directly on the glass substrate and for etching off the EC layer on the transparent electroconductive layer, respectively, vary from each other. This is particularly true where the etching is carried out by the employment of a dry etching method such as sputtering etching and plasma etching techniques. This results not only in reduced definition of the pattern to be, or being, displayed, but also in an increased possibility of blackening of the transparent electroconductive layer during the practice of the etching.
Similar problems as discussed above are also present in the practice of the baking method used to form the EC layer. Specifically the employment of the baking method results in the formation of the EC electrode layer directly on the glass substrate at an area where no pattern is formed and, if the EC layer is baked while it is, burning or evaporation of an unnecessary portion (i.e., not patterned portion) of the EC layer would take place unevenly under the influence of a glass, resulting not only in reduced definition of the pattern to be, or being, displayed, but also in formation of a matter which would disturb the function of the EC material.